Project Summary/Abstract Electronic Nicotine Delivery Systems (ENDS) can be modified by consumers in ways that are intended by the manufacturers (for example, adjusting the voltage using the built-in dial on the product) and in ways for which the product was not designed (such as replacing the battery with a more powerful one, directly dripping e-juice on the coil to produce thicker clouds of aerosol, or using ENDS to consume other substances, such as alcohol or cannabis). In evaluating whether ENDS or other new tobacco products harm or benefit the population as a whole, FDA assesses how people in the real world use these products, including how they modify (alter, customize, misuse, tamper with, or adjust) them. Consumer modifications can significantly impact the appeal, addictiveness, and toxicity of tobacco products, and thus, their population harm. Furthermore, youth and young adults might find modifications more appealing than older adults. Thus, the ability to modify products opens up new issues in evaluating whether a product should be allowed on the market and what types of product standards may be appropriate in order to prevent and reduce their use by youth and encourage their use by older adults trying to quit cigarette smoking. But, little is known about how and why consumers modify ENDS, how much modification is occurring, and what design characteristics lead to these modification activities. Thus, the impact of product design characteristics on modification needs to be further investigated. We will identify the various ways users modify ENDS (Aim 1) by interviewing ENDS enthusiasts, examining the content of social media (YouTube and Reddit) for portrayals and discussions of ENDS modifications, and conducting focus groups with young and older adult ENDS users and individual interviews with youth ENDS users. This qualitative research will inform the development of the questionnaire that will be administered to nationally representative samples of youth, young adults, and older adults in order to determine the extent that modification of ENDS occurs in the U.S. population (Aim 2). Information gained from both qualitative and quantitative phases of research will allow us to evaluate the role of ENDS product characteristics that lead to modification and what motivates these activities (Aim 3). This project will provide evidence to help guide public health policy and regulatory decision-making for new product review and product standards.